Radiocommunication



Dec. 10, 1935.

H. S. POLIN RADIOCOMMUNICATION Filed Nov. 25, 1931 Patented Dec. 10,1935 NH'E'ED STTES eArENT OFFICE 8 Claims.

This invention relates to apparatus for the generation of sustainedoscillations of extremely high frequencies, corresponding toperiodicities of the order of thirty to one hundred thousand kilo-cyclesor more; and to the utilization of such apparatus for purposes of shortWave communication by radio or over electrical conductors.

An object of the invention is to provide a tuned thermionic oscillationgenerator operable at the frequencies specified, characterized in thatthe periodicity of oscillation may be predetermined and controlled insubstantial independence of the electrical circuits requisite forenergization of the thermionic element, or for the radiation of thegenerated high frequency energy.

A further object of the invention is to provide a tuned ultra-highfrequency generator, employing standard parts, the operation of whichmay, from time to time, be duplicated, either with the same apparatus,or with similar apparatus constructed in accordance with manufacturingtolerances common to the type of equipment employed.

Another object of the invention is to provide a system of short wavecommunication between two or more stations, each radiating continuouslyat a common extremely high carrier frequency, the several stations beingso arranged that twoway intercommunication may be carried oncontinuously between stations at the common carier frequency and atenergy levels exceeding those heretofore obtainable at the wave lengthsin question.

Although various systems are known for the generation of electricaloscillations within the short wave range contemplated by this invention,all such proposals are variously objectionable, (l) as failing tosustain oscillations at apprecipower outputs for wave lengths down to afrac= n of a meter, (2) as being generally seriously limited as to theavailable power output, (3) as being unstable and unreliable inoperation, (4) as providing oscillatory energy the frequency of which,particularly the upper limiting frequency, is largely determined by theconstants of the electrical apparatus employed, such as the thermionicdevice and the requisite associated circuit elements, and therefore asnot depending for operation upon criteria by which the periodieity maybe predetermined, controlled and duplicated in substantial independenceof unavoidable variations in such constants, and (5) as not beingadapted to tuning whereby the periodicity may be arbitrarily adjusted atwill throughout a range in frequency.

In contrast to these defects the present invention provides anoscillation generator which inherently provides a relatively largeavailable power output adjustable at will both in amplitude and infrequency. By associating wave radiat- 5 ing, signal modulating anddetecting means with a plurality of oscillation generators, inaccordance with the present invention, remotely located for purposes ofcommunication, and by causing the several resulting stations to generatehigh 10 frequency oscillations and so react upon each other as to remainin exact syntony, a system of standing waves in space may be establishedbetween stations, which is a measure of the potential or stored-up highfrequency energy of the 15 several stations, available at each stationfor purposes of signal transmission and reception.

As a result of these standing waves each station reacts upon every otherstation, and the high frequency energy generated at a given station 20may thus be made available at all other stations for amplifying thesignal. Apparently at any given station of a system in accordance withthe present invention, the amplitude of the carrier frequency generatedthereat is enhanced 25 to the extent of the aggregate amplitudes of theseveral carrier waves emanating from the other stations which are pickedup by the local antenna. Accordingly, modulation of this resultantamplitude in transmitting produces a greater modulated carrier wavesignal output than would be obtained in the absence of these receivedenergies. Likewise in receiving, the amplitude of carrier oscillation issimilarly enhanced, and the detected wave correspondingly amplified.

The manner in which the present invention achieves the novel resultsabove pointed out is best explained by reference to the single figure ofthe drawing wherein there is shown diagrammatically a pair of highfrequency units in accordance with the present invention, each unitembodying an oscillation generator together with the requisite signaltransmitting, receiving and modulating apparatus for effecting two-wayintercommunication between units.

Referring to station I shown at the left in the figure, the circuitemploys a vacuum tube 2 having an anode A, a filament or cathode K and acontrol grid S. Tube 2 is energized from a direct current source G, thenegative terminal of which 50 is connected through a high frequencyblocking impedance 5 to one side of the cathode K. The positive terminalof source I is connected through a magnetron coil 8 surrounding tube 2,to the other side of the cathode through blocking im- 55 pedance 6 andresistance 9; and also over conductor IE] to the anode A. The potentialdrop across resistance 9 applies the necessary positive operatingpotential to the anode A of the tube.

The grid S is connected over conductor II to the negative side of thecathode. A signal modulating device I2, such as a microphonetransmitter, energized over conductors I3 by the potential drop acrossthe cathode K, is coupled through transformer T1 to the grid conductor,for purposes of modulating the high frequency carrier in accordance withsignaling currents. Similarly a receiving element M, such as a pair ofheadphones, is coupled to the anode conductor I through transformer T2for indicating the rectified component of the modulated carrier wave,detection of which is effected through the action of the grid leak I'Iincluded in the grid conductor I I. 7

High frequency blocking impedances 3 and 4 are included in the gridconductor II and the anode conductor I0, respectively, for restrictingthe high frequency oscillatory currents within their proper paths aswill now be explained.

The portion of the system responsible for the periodicity of thegenerated high frequency 05- cillations comprises, reduced to itsessentials, circuit I5 consisting of the effective capacity C1 of theextremely small variable condensers I6 and I3 connected in parallel byshort leads directly between grid S and anode A of tube 2, together withthe connecting leads and the resultant capacity C2 of the interelectrodecapacities of the tube which are effective between grid and anodeelectrodes. The periodicity f of this circuit is determined by itseffective series capacity C and inductance L, substantially inaccordance with the formula:

The inductance L is that of the closed loop I5, which is of extremelysmall physical dimensions. The capacity C which is the effectivecapacity of condensers C1 and C2 in series is given by the formula:

It is apparent from Formula (2) that the effective capacity C can neverexceed the grid-to-anode capacity C2, no matter how large the tuningcondenser C1 may be made. It is likewise apparent from Formula (2) thatif the variable condenser C2 is made small in comparison with thegrid-toanodecapacity C2, say, of the order of one-tenth C1 or less, thenthe effective capacity C will become substantially equal to C1.

The significance of this is that if the magnitude of condenser C1 ismade comparable to or smaller than that of C2, the former will have acontrolling influence on the periodicity of oscillation in loop I5. Bymaking C1 variable as'shown in the drawing, the periodicity ofoscillation may be adjusted throughout a relatively wide continuousfrequency range of the order of 100,000 kilo cycles. As a result offrequency adjustment thus provided, tubes of standard construction, theelectrical constants of which vary from tube to tube in accordance withthe usual manufacturing tolerances, may be utilized in the circuitwithout necessitating a departure from the frequency at which it isdesired to operate.

The extremely short wave lengths to which the circuit of the presentinvention may be ad- .iusted, result from the facts that the inductanceL is inherently extremely small, whereas the effective capacity C, is,for reasons stated, reduced below that of the tube interelectrodecapacities. The circuit of the present invention has in fact beenutilized for the production of sustained 5 oscillations corresponding towave lengths down to a small fraction of a meter.

It is well known that a necessary condition generally for themaintenance of sustained oscillations in a vacuum tube circuit, is thatthe 10 oscillatory circuit must be so coupled to the tube thatoscillations in the circuit will cause the grid and anode of the tube toassume opposite instantaneous polarities with respect to the filament orcathode. With the circuit of the presl5 ent invention wherein theoscillatory circuit I5 is coupled to the tube through the grid-anodeimpedance, it will be seen that this condition is necessarily satisfiedprovided at the frequency of oscillation the effective impedance betweengrid and cathode, is of the same character, 1. e. has the same reactancesign, as the effective impedance between cathode and anode. If the oneimpedance is capacitive the other must likewise be capacitive.

A second condition requisite to the maintenance of sustainedoscillations is that tube 2, arranged in circuit as shown, must becapable of providing an impedance as measured between the grid and anodeelectrodes which contains a negative resistance component at least asgreat as the efiective energy absorbing resistance of the oscillatorycircuit. If this condition is satisfied, the oscillations will increasein amplitude until the negative resistance between grid and anodeelectrodes of the tube becomes equal in magnitude tothe energy absorbingresistance of the oscillatory circuit. This variation in negativeresistance component of the tube with amplitude in oscillation occurs byreason of the curvature in the grid voltage-plate current characteristicof the tube, i. e. its mutual conductance, whereby the systemautomatically adjusts itself to stability of oscillation both inamplitude and in frequency.

It has been observed that inclusion of resistance I9 in the circuitrenders the generation of oscillations extremely stable in bothamplitude and frequency. This suggests the possibility that at theextremely high frequencies in question resistance I9 may partake of thenature of a crystallographic control. Although it is impossible tosettle this point definitely in the absence of suitable measuringapparatus operable at the frequencies in question, some support for thisview results from the high value of resistance I9 employed. It is wellknown in this connection'that extremely high resistance units evidencepeculiarities of operation not noticeable in resistance elements of lowmagnitude.

In order to supplement the oscillatory action due to the directimpedance coupling provided by the grid-to-anode capacity between loopI5 and vacuum tube 2, a magnetron coil 8 may be included in the anodecircuit as shown in the drawing.

A convenient method for withdrawing oscillatory energy from orimpressing oscillatory energy upon loop I5 is provided by the triplatecondenser I8, of extremely small capacity, comparable to that ofcondenser I6. The external plates of condenser I8 are connected directlyto the grid and anode respectively of tube 2. The intermediate plate 20of condenser I8 may be connected by operation of a switch 30 to acondoctor 2! which extends to .the corresponding switch 30 forconnecting conductor 21 to plate 2c of the analogous system l at theright of the figure for purposes of intercommunication. 01' plate 26 maybe extended directly to an antenna by alternative operation of switch S,.in which event system I would be connected by means of switch S with asimilar antenna A'.. The external plates of condenser l'8 are relativelyadjustable for the purpose of adjusting the constants of the oscillatorycircuit.

The intermediate plate 20 of condenser l8 serves the purpose ofimpressing upon the conductor M, or an antenna, a desired fraction ofthe total available output energy of loop With the foregoing analysis inmind, operation of the system to transmit and receive signals may bebriefly explained. Modulating frequencies originating in device 12 areimpressed upon the grid electrode S through transformer T1, causingthereby the amplitude of high frequency oscillations existing in loop [5to vary in accordance with the modulating frequencies. The resultingmodulated carrier wave is propagated to system i where it is impressedthrough condenser l8 upon circuit H5 in which oscillations arecontinuously generated and sustained by tube 2' at the carrierfrequency. Due to the presence of the grid leak I1, there results ademodulation of the resulting frequencies impressed upon tube 2, as aconsequence of which signaling frequency flows in the anode conductor itand is thereby impressed through transformer T2, upon the headphones l4.

Referring to the drawing, an analysis of the circuit will show that thehigh frequency energy generated at station in circuit I5, is propagatedto and impressed directly upon the analogous circuit l5 at station I,likewise generating high frequency oscillations. In the same Way highfrequency energy generated in circuit I5 is propagated to and impressedupon circuit I5. In this way the thermionic oscillation generators atstations I and l react upon one another through the intervening wavepropagating media. Due to the non-linear operating characteristicsinherent in the thermionic elements 2 and 2, the oscillation generatorswill, in a manner known, fall into step at a common carrier frequencyprovided they are adjusted to oscillate sufficiently close to the commonfrequency independently of one another.

It appears probable that the resistances l 9 and i9 assist in thisfalling into step, since it has been observed that their presencefacilitates tuning remote stations to the common carrier frequency andin the maintenance of sustained oscillations at that frequency.

Due to the fact that each station generates and radiates, in the mannerexplained, at a common carrier frequency, a system of standing waves inspace will necessarily be produced between stations, resulting from thesuperposition of waves oppositely propagated at a constant velocity. Thehigh frequency energy available at each station for purposes of signalpropagation is thus enhanced to the extent of that received thereat fromeach of the remotely located stations.

The multiple amplification thus imparted to the received signal byoperation in accordance with the principles of the invention as outlinedis of extreme importance in the field of short wave communication, due(1) to the limited power output which short wave oscillators generallyare capable of providing, and (2) to the fact that no'means are atpresent known capable of providing straight amplification at thefrequencies or wavelengths under consideration.

I claim as my invention:

1. An oscillation generator comprising a condenser connected betweengrid and anode electrodes of a thermionic tube forming thereby inconjunction with the inherent inter-electrode tube capacities, anoscillatory circuit the natural periodicity of which is regulated bysaid condenser, and means connecting said anode and grid to the cathodeof said tube for producing sustained oscillations in said circuit, saidanode connection including a magnetron coil.

2. A short wave combined radio transmitter and receiver comprising atriplate condenser, the several plates of which are relativelyadjustable for varying the capacities therebetween, conductors extendingfrom the external plates of said condenser to the grid and anodeelectrodes respectively, of a thermionic tube forming thereby inconjunction with the inherent inter-electrode tube capacities, anoscillatory circuit the periodicity of which is regulated by saidcondenser, connections from grid and anode respectively, to the cathodeof said tube for causing sustained oscillations in said circuit of theperiodicity thereof, signal transmitting and receiving means interposedin said connections respectively, and wave radiating means connected tothe intermediate plate in said condenser.

3. A short wave radio transmitter and receiver comprising a condenserconnected between grid and anode electrodes of a thermionic tube formingthereby in conjunction with the inherent interclectrode tube capacities,an oscillatory circuit the periodicity of which is regulated by saidcondenser, means connecting said grid and anode to the cathode of saidtube for producing sustained oscillations in said circuit, said anodeconnection including a magnetron coil signal transmitting and receivingmeans interposed in said connections respectively, and wave radiatingmeans coupled to said oscillatory circuit.

4. A short wave radio transmitter and receiver comprising, a triplatecondenser, the several plates of which are relatively adjustable forvarying the capacities therebetween, meansconnecting the external platesof said condenser respectively to the grid and. anode electrodesrespectively, of a thermionic tube, a second variable condenserconnected between said grid and anode electrodes, said condensers andconnections, together with the inherent interclectrode tube capacitiesforming an oscillatory circuit the periodicity of which is regulated bysaid condensers, connections from said grid and anode respectively, tothe cathode of said tube adapted to cause sustained oscillations in saidcircuit, signal transmitting and receiving means interposed in saidconnections respectively, and Wave radiating means connected to theintermediate plate of said triplate condenser.

5. Short wave generating and signalling apparatus comprising, athermionic tube having an anode, a cathode and a grid, a connectionbetween anode and grid, adjustable capacity serially interposed in saidconnection forming together with the interclectrode capacities of saidtube an oscillatory circuit the periodicity of which is regulated bysaid adjustable capacity, connections from said anode and gridrespectively to said cathode, choke coils interposed in said connectionsadjacent said anode and grid, signal modulating and grid biasing meansinterposed in said grid connection, signal indicating means interposedin said anode connection, and wave radiating means capacitively coupledto said adjustable capacity.

6. Short wave generating and signalling apparatus comprising, athermionic tube having an anode, a cathode and a grid, a connectionbetween anode and grid, capacity, including a triplate condenser havingits external plates connected to said anode and grid, seriallyinterposed in said connection forming together with the in'terelectrodecapacities of said tube an oscillatory circuit, wave radiating meansconnected to the intermediate plate of said tri-plate condenser,connections from said anode and grid respectively, to said cathode,choke coils interposed in said connections adjacent said anode and grid,signal modulating and grid biasing means interposed in said gridconnection, and signal indicating means interposed in said anodeconnection.

7. Short wave generating and signalling apparatus comprising, athermionic tube having an anode, a cathode and a grid, a tri-platecondenser having its external plates connected to said anode and gridrespectively, and its intermediate plate connected to wave radiatingmeans, a resistance in shunt to said tri-plate condenser between saidanode and grid, connections from said anode and grid respectively tosaid cathode, choke coils interposed in said connections adjacent saidanode and grid, signal modulating and grid biasing means interposed insaid grid connection, and signal indicating means interposed in saidanode connection.

8. Short wave generating and signalling apparatus comprising, athermionic tube having an anode, a cathode and a grid, a tri-platecondenser having its external plates connected to said anode and gridrespectively, and its intermediate plate connected to wave radiatingmeans, a second condenser in parallel with resistance connected betweensaid anode and grid, connections from said grid and anode respectivelyto said cathode, choke coils interposed in said connections adjacent theanode and grid respectively, signal modulating and grid biasing meansinterposed in said grid connection, and signal indicating meansinterposed in said anode connection.

HERBERT S. POLIN.

